Apparatus for the recording of asymmetric or normal sound films



O. K. KOLB ETAL 20 APPARATUS FOR THE RECORDING 0F ASYMMETRIC OR NORMAL:SOUND FILMS Feb. 25, 1941 2 Sheets-Sheet '1 ,Filed Jan. 50, 1940 FIG. 21

Feb. 25, 194i.

0. KOLB ETAL APPARATUS FOR THE RECORDING OF ASYMMETRIC OR NORMAL SOUNDFILMS Filed Jari. 50, 1940 2 Sheets-Sheet 2 FIG.

Patented Feb. 25, 1941 PATENT OFFICE APPARATUS FOR THE RECORDING OFASYMlVIETRIC OR FILMS NORMAL SOUND Otto Kurt Kolb, Chiswick, London, andAlbert Stanley Pratt, London, England, assignors to British AcousticFilms Limited, London, England, a British corporation ApplicationJanuary 30, 1940, Serial No. 316,308 In Great Britain March 9, 1939 5Claims.

This invention relates to sound recording apparatus and moreparticularly to apparatus arranged to record either asymmetric or normalsound records. The asymmetric sound records produced by our improvedapparatus are of the kind in which, on opposite halves of the soundtrack zone, there are recorded separate sound tracks which are in mutualcounterphase, but which are each individually formed by symmetrical wavetraces, so that on each said lateral zone the record produced is acomplete double-hump registration of the recorded wave train.

For the production of records of the asymmetric or push-pull type, ithas been previously proposed to arrange two separate oscillographs eachworking in counterphase as regards the phonic current input, but actingin phase as regards a bias controlling current; each oscillograph has,therefore, produced a complete noiseless record trace in known mannerand the two oscillcgraphs have been so disposed in relation to a singlecombining objective optical system that the two record pencils producingtraces have been projected side by side upon the sound track on therecording film.

According to the present invention apparatus for producing aphotographic sound record either of the asymmetric or of the normalvarying width constant density type, includes a single oscillograph, twomasks each bearing one or more triangular apertures, and means formoving the said aperture masks in opposite directions in accordance withthe intensity of the sound being recorded.

In conjunction with the single oscillograph there are arranged twomovable masks, each bearing a triangular or multiple triangularaperture. By multiple triangular aperture is meant an aperturecomprising a number of similar triangular components side by side forproducing multiple traces such as could be used for making multipletrace normal double-hump sound records. For the production of asymmetricsound records, however, it is preferred to employ only two apertures,one on each mask, the two masks being arranged to be moved parallel orsubstantially parallel to each other, but in opposite directions, bymeans of a suitable drive unit or units to which is applied a current,or potential varying in accordance with the mean amplitude, peak orenvelope variations of a recorded wave train.

The two masks referred to may be connected by means of a suitablemechanical linkage so that the triangular apertures formed in them aremoved parallel to themselves and bothmasks. The two masks may be movedby means of a single drive unit to which the bias or control current, orpotential varying in the manner set forth may be applied. a

Light is projected through the apertures in the two movable masks from asuitable source, such as an exciter lamp, on to the mirror of the singleoscillograph and thence on to a fixed mask bearing a linear slit.

When asymmetric records are being produced images of the two triangularapertures are formed upon this slit by means of optical lenses whichimages with increasing sound amplitudes, are moved in oppositedirections at right angles 16 to said slit, but which, being reflectedfrom the oscillograph mirror, vibrate at phonic frequencies in unisonacross said slit.

As the apices of the two triangles lie in opposite directions, the twolight pencils passing through the slit, where it is covered by the0pposed triangularirnages, vary in length in such a manner that thecorresponding collinear images formed upon the recording film sweep outsymmetrical wave traces in exact counterphase,

whilst the mean width of each individual sound track on the two lateralzones is dependent upon the position in which the corresponding primarymask is moved by the shift or bias controlling current or potential.

The two oppositely movable primary masks may be mounted in a suitablefixture together with their drive unit or units, and this fixture may beeither made withdrawable, so that it may be replaced by one bearing asingle movable mask having a triangular or multiple triangular aperturefor the recording of normal films, or one .of the two movable masks of apair may itself be formed with an additional aperture or apertures sothat the fixture, as a whole, may 40 be moved into a second operativeposition in which the images of the aperture or apertures in one maskalone may be thrown upon the recording slit for the purpose of effectingrerangement for moving the recording masks in opposed directions; and

Fig. 3 partly in side elevation and partly in vertical cross-section apreferred arrangement in which two recording masks are moved in opposeddirections by a single moving coil drive unit, the whole arrangementbeing adapted to be shifted in relation to the recording light beam forthe purpose of alternatively recording asymmetric or normal films.

In Fig. 1 light from a suitable source such as a lamp I is projected bymeans of an optical system 2 through apertures 31) and 4a, formed inmasks 3 and 4, on to the mirror 5a of oscillograph 5, so as to produceon secondary mask 6 images of the two apertures 3b and 4a. The

mask 6 bears a transverse slit 6a and light passing through this slit isprojected by means of objective system I on to sound track 8a of film B.It will be seen that if the oscillograph 5 is stationary and the twomasks 3 and 4 are moved in opposite directions, the two images 3b and 4aformed upon the mask 6 are moved over the slit 6a in opposite directionsso that the average breadth of the light strip relating to each imageand passing through the lens system 'I is increased or diminished as thecase may be. When, however, the oscillograph mirror 5a vibrates thelight pencil representing one image is increased whilst the other isdiminished and vice versa, so that the associated sound traces arerecorded in exact counterphase.

Referring to Fig. 1 it will be seen that the two masks 3 and 4 aremounted upon rods 9 and III which are linked by lever II and supportedby parallel motion springs I2, I3 and I4. One of the rods, for example9, is connected to a moving coil I5 which is disposed in the annular airgap I 6a of a pot magnet I6.

The windings of moving coil I5 are traversed by a bias or controllingcurrent produced in known manner, which varies in accordance with themean intensity or peak amplitude or envelope variations of a sound to berecorded.

In Fig. 2 a similar arrangement of the two masks 3 and 4 is indicated,but in this case eachof the rods 9 and I is connected to separate movingcoils I and I5a and is supported by parallel motion spring systems I2,I4 and I2a, I4a respectively. In this case the bias currents passingthrough the two moving coil arrangements I5 and I5a are either reversedin phase or the magnetic field in which one of them is disposed isreversed in sense to that of the other so that the two masks, with onedirection of bias current flow, move in opposite directions.

In Fig. 3 an arrangement similar to thatin Fig. 1 is shown partly incross-section, the masks being mounted in a complete combined unitcomprising the pot magnet I6 supporting frame I! and the mechanicallinkage constituted as before described. In this arrangement the twomasks are driven in unison by the single coil I5. In this case, however,the magnet I6 is constructed upon a base I8 which slides upon a fixedsupport I9. An indexing lever '20, has a termination 20a, formed as anindex finger, which engages one or the other of the two notches I 9a andI9!) formed in the support I9. This arrangement serves to index orlocate definitely in two alternative positions the mask system, so thateither an image of the apertures 3b and 4a is formed upon mask 6 whenasymmetric recording is in progress, or if mask 3 alone is brought intothe recording light beam then an image of the apertures 3a, 3b is formedupon the said mask 6 so that a normal sound record of the twindoublehump noiseless variable area type is recorded. Alternatively, thearrangement could be such as to enable the aperture 40. alone to bebrought into the recording light beam for producing a normal soundrecord of the ordinary doublehump noiseless variable area type.

What is claimed is:

1. Apparatus for producing photographic sound records of the asymmetricand of the normal varying width constant density type, including asingle oscillograph, two masks each bearing at least one triangularaperture, 9. source of recording light beam, means for selectivelymoving one or both masks with their apertures in the path of the lightbeam to permit the production of sound records by employing one or bothmasks, and means for moving said masks in opposite directions withrespect to one another in accordance with the intensity of the soundbeing recorded.

2. Apparatus according to claim 1, wherein electromagnetic means areprovided for moving the aperture masks with respect to one another.

3. Apparatus according to claim 1, for producing an asymmetric soundrecord wherein the means for moving the masks in opposite directionscomprise spring supported rods carrying the said masks, a lever throughwhich said rods are linked, and a pot magnet having a moving coilconnected with one of said rods, said moving coil being energized inaccordance with the intensity of the sound being recorded.

4. Apparatus for producing photographic sound records of the asymmetricand of the normal varying width constant density type, including asingle oscillograph, two masks each bearing at least one triangularaperture, a source of recording light beam, means for selectively movingone or both masks with their apertures in the path of the light beam topermit the production of sound records by employing one or both masks,means for moving the masks in opposite directions with respect to oneanother comprising spring supported rods carrying said masks, and amoving coil within a pot magnet connected with each of said rods, saidmoving coils being energized in accordance with the intensity of thesound being recorded.

5. Apparatus according to claim 4, a base carrying the masks and themagnet, and the means for positioning the masks relatively to the lightbeam comprising a support upon which said base slides.

OTTO KURT KOLB. ALBERT STANLEY PRATT.

